I never set out to be a series author. My very first thriller, The Perfect Husband, was inspired by infamous serial killer Ted Bundy. To catch my escaped killer/vengeful husband, I created an FBI profiler, Pierce Quincy, who became so popular with readers I ended up writing an entire FBI Profilers series. It was a pattern I then repeated with Boston detective D.D. Warren, victim-turned-vigilante Flora Dane, and, somewhere in between, private investigator Tessa Leoni. Pretty soon, it seemed there wasn’t any crime my fictional stable couldn’t handle. My writer’s attention would be grabbed by some stranger-than-fiction real-world wrongdoing, and the next book staffed itself.

Then one day I read an article on Lissa Yellowbird-Chase, an ordinary woman dedicated to doing the extraordinary: finding missing people the rest of the world has forgotten. And just like that, I knew the story I had to write: one that by definition couldn’t involve any of my previous series characters; one involving a very real, very everyday human, who wants to do the right thing.

I know life isn’t fair—that for every blue-eyed blonde whose disappearance grabs national headlines, there are thousands of other missing persons we never hear about. But I hadn’t understood the magnitude of the disparity: how children of color are much more likely to be classified as runaways, even when they’ve fallen victim to human traffickers, or how a kid can vanish from an economically disadvantaged neighborhood with no Amber Alert or media coverage.

For previous novels, I used federal resources such as the National Center for Missing and Exploited Children for research. Now, I learned about the Black and Missing Foundation, whose database of cold cases makes for heartbreaking reading. These are the cases that fall through the cracks. These are the cases that, more and more, are being picked up by private crusaders eager to get the job done.

This initial background helped me create amateur sleuth Frankie Elkin, a recovering alcoholic whose life is short on belongings and long on regret. Stable job? White picket fence? Long-term relationships? She tried and failed. Now she leads a sort of “anti-life,” roaming from town to town in order to solve cold missing persons cases.

You’d think writing about a “normal” person doing investigative work would be easier than writing my previous thrillers, which involved research at such places as the Body Farm, Quantico, and plenty of prisons. It wasn’t. After decades of writing police procedurals, having to think in terms of what an amateur could do to advance a cold case was incredibly challenging.

So what do the Lissa Yellowbird-Chases bring to the fiction table? They bring good listening skills; real-world social engineering; and a willingness to make the effort to go out into the community and meet with family, friends, and neighbors and, person-by-person, learn about the victim. Most official investigative efforts start with general probabilities about who, what, when, where, why, and how. Amateur efforts, by definition, focus on individuality—this one person, this lone event, this singular disappearance. It’s an intriguing, and often impactful, difference.

Having said that, I quickly realized I couldn’t write an amateur-sleuth novel without conducting my traditional police interviews. This time, however, proper police procedure didn’t serve as plot points to drive my book forward but instead became the basis of my initial puzzle. For example, how does the average 15-year-old girl, armed with a cellphone and social media addiction, go missing from a dense urban environment filled with potential witnesses and constantly recording surveillance cameras? Then there’s license-plate-reading technology, which can be used to identify all vehicles in the area at the time of disappearance. Snapchat, “finstagram” accounts, and all the various other teen-centric communication methods used for secrecy—all can be recovered given enough time and effort. Meaning the more I spoke with experts, the deeper I disappeared down the rabbit hole. Forget how my amateur sleuth Frankie Elkin would find missing 15-year-old Angelique Badeau—how the hell had the girl disappeared in the first place?

Which is where the more things change, the more things stay the same. My inspiration behind Before She Disappeared was different. My research varied. But the end process—planting my butt in a chair and writing, writing, writing—remained the same. What happened to Angelique? How can Frankie find her 11 months later? And why is Frankie doing this anyway? Those questions became my reasons to show up to work every day and write some more.

Frankie Elkin is my new favorite character. And if you also like her, then, most likely, my first standalone thriller in 20 years will become the beginning of my next series. You never know.

Lisa Gardner is the bestselling author of 23 novels, including The Neighbor, which won Thriller of the Year from the International Thriller Writers. She lives in New Hampshire with her family.